ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
493 
For instance, Z. nana and Muelleri are more easily distinguished the one 
from the other by the structure of their stem than by their leaves. 
Inversely, however, Z. nana and Capricorni show more difference in the 
structure of their leaves than in that of their stem. 
Spiral Phyllotaxis.* * * § — Herr B. Rosenplenter points out that in tho 
germination of dicotyledonous seedlings there must be either a single 
primary leaf or a primary pair. In the first case there is only one plane 
of symmetry, which bisects the angle of the median planes of the coty- 
ledons. In the second case there are either two planes of symmetry, or 
only one which corresponds with the common median plane of the 
cotyledons. The various special modifications of these cases are described 
in detail. 
Leaf-spirals in the Coniferse.f — Herr A. Weisse treats from a mathe- 
matical point of view the turning of the leaf-spiral and the nature of 
the pressure which causes it in the axillary buds of Coniferee. In 
the axillary buds of by far the greater number of Coniferse with spiral 
phyllotaxis, the third leaf faces the stem. The lateral deviations depend 
upon three causes — a lateral displacement caused by the supporting leaf, 
a lateral insertion of the supporting leaf, and the pressure of the bases 
of the adjacent leaves of the mother-shoot which stand above the sup- 
porting leaf. 
Influence of Light on the production of Spines. :£ — M. A. Lothelier, 
in a former paper, made some observations on the influence of the hygro- 
metric state of the air on the production of spines, and in the present 
paper studies the influence of light in the same relationship. Various 
examples are taken, for instance : — Berberis vulgaris, Bobinia pseudacacia, 
JJlex europseus, Cratsegus oxyacantlia , and Bibes uva-crispa, the general 
conclusion being that stronger light causes the formation of more 
numerous, better-developed, and more differentiated spines. 
Bulbs and Tubers in the Juncacese.§ — Herr F. Buchenau describes 
the formation of tubers and bulbs in various species of J uncus and Luzula. 
They are produced either by the larvae of animals or by fungi. In the 
latter case the parasite is a species of Schinzia or EntorrMza , S. Cas- 
paryana or digitata. 
Growth of Root-hairs. || — M. H. Devaux has already shown that light 
is favourable to the development of root-hairs. Observations on the root 
of Lolium perenne were made, and it was found that the minimum growth 
took place between midday and two o’clock. The maximum growth of 
the rootlets, however, took place in the region of the root formed during 
the day, and the minimum in that formed during the night. A certain 
equilibrium is thus maintained between the growth of the root-hairs 
and that of the root itself. 
* ‘Ueb. d. Zustandekommen spiraliger Blattstellungen b. dikotylen Keim- 
pflanzen,’ Berlin, 1890, 43 pp. and 1 pi. See Bot. Centralbl., xlv. (1891) p. 346. 
f Flora, lxxiv. (1891) pp. 58-70 (1 ph). 
j Comptes Rendus, cxii. (1891) pp. 110-2. Cf. this Journal, ante, p. 214. 
§ Flora, lxxiv. (1891) pp. 71-83 (2 figs.). 
|| Bull. Soc. Bot. France, xxxviii. (1891) pp. 51-2. Cf. this Journal, 1888, p. 995. 
